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首页> 外文期刊>Biochemistry >Structural features and light-dependent changes in the sequence 306-322 extending from helix VII to the palmitoylation sites in rhodopsin: a site-directed spin-labeling study.
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Structural features and light-dependent changes in the sequence 306-322 extending from helix VII to the palmitoylation sites in rhodopsin: a site-directed spin-labeling study.

机译：结构特征和光依赖性变化在视紫红质中从螺旋VII延伸到棕榈酰化位点的序列306-322：定点自旋标记研究。

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摘要

Sixteen single-cysteine substitution mutants of rhodopsin were prepared in the sequence 306-321 which begins in transmembrane helix VII and ends at the palmitoylation sites at 322C and 323C. The substituted cysteine residues were modified with a selective reagent to generate a nitroxide side chain, and the electron paramagnetic resonance spectrum of each spin-labeled mutant was analyzed in terms of residue accessibility and mobility. The periodic behavior of these parameters along the sequence indicated that residues 306-314 were in a regular alpha-helical conformation representing the end of helix VII. This helix apparently extends about 1.5 turns above the surface of the membrane, with one face in strong tertiary interaction with the core of the protein. For the segment 315-321, substituted cysteine residues at 317, 318, 320, and 321 had low reactivity with the spin-label reagent. This segment has the most extensive tertiary interactions yet observed in the rhodopsin extra-membrane sequences at the cytoplasmic surface. Previous studies showed the spontaneous formation of a disulfide bond between cysteine residues at 65 and 316. This result indicates that at least some of the tertiary contacts made in the 315-321 segment are with the sequence connecting transmembrane helices I and II. Photoactivation of rhodopsin produces changes in structure detected by spin labels at 306, 313, and 316. The changes at 313 can be accounted for by movements in the adjacent helix VI.
机译：制备了视紫红质的十六个单半胱氨酸取代突变体，其序列为306-321，其起始于跨膜螺旋VII，终止于322C和323C的棕榈酰化位点。用选择性试剂修饰取代的半胱氨酸残基以产生一氧化氮侧链，并根据残基可及性和迁移率分析每个自旋标记突变体的电子顺磁共振谱。这些参数沿着序列的周期性行为表明残基306-314呈规则的α-螺旋构象，代表螺旋VII的末端。这种螺旋线显然在膜表面上方延伸了大约1.5圈，其中一个面与蛋白质的核心形成强三级相互作用。对于区段315-321，在317、318、320和321的取代的半胱氨酸残基与自旋标记试剂的反应性低。该区段在细胞质表面的视紫红质膜外序列中观察到最广泛的三级相互作用。先前的研究表明，在65和316处的半胱氨酸残基之间会自发形成二硫键。该结果表明，在315-321片段中形成的至少三级接触具有连接跨膜螺旋I和II的序列。视紫红质的光活化产生了由自旋标记在306、313和316处检测到的结构变化。在313处的变化可以由相邻螺旋VI中的运动来解释。

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